1. Field of the Invention
This invention relates to a casing of a blower and, a ventilating fan utilizing such casing, and more particularly it, to a novel casing construction for making it possible to readily fabricate a blower casing which is complex in construction and complicated in production process steps because of the presence of many curved surfaces and a ventilating fan utilizing such casing construction.
2. Description of the Prior Art
It has been usual practice to produce a casing of a blower by molding a synthetic resinous material into spiral cases or making thin plates into spirial cases by thin plate working and then installing the spiral cases in a frame. The former method requires a mold for producing the spiral case which, in many cases, is very expensive. When the latter method is relied on, the spiral cases are produced in several parts, such as wind tunnel portions and flange portions, and these parts are assembled and joined together by spot welding or caulking. Thus, the latter method requires a plurality of process steps for fabricating the spiral cases. However, the spiral cases formed of synthetic resinous material or fabricated by thin plate working suffer the disadvantage that they transmit the vibration of a motor or a fan located in the vicinity thereof. And further an air current generated by operation of the blower causes resonance of the spiral cases, so that when it is desired to reduce the noise level of the ventilating fan it is necessary to use various types of vibration preventing material or reinforcing material in addition to attaching sound absorbing material to the frame. The spiral cases formed of synthetic resinous material or fabricated by thin plate working to have the aforesaid construction are assembled, in the final step, with the frame and secured thereto by screws and nuts, so that the assembling operation is a time-consuming operation.
Proposals have been made to use a method whereby spiral cases produced by using foamed synthetic resinous material and pasted to a frame or a method whereby a frame itself is utilized as a part of the mold for forming spiral cases in the frame by using foamed synthetic resinous material. However, if these methods are used, in case of the former it would be impossible to simplify the production steps and in case of the latter it would be impossible to simplify production facilities.